A screwdriver is a handy and helpful tool for use in tightening or loosening a screw. The conventional screwdriver is generally made up of a handle and a shank having a head tip for turning a screw. Among several kinds of screwdrivers in existence today, the best-known screwdrivers include the screwdriver with a cross-shaped head tip for turning a Phillips screw that has two slots crossing at the center of the screw head, and the screwdriver with a slotted head tip that fits into the slot in the head of a slotted screw.
The prior art screwdrivers described above are generally defective in design in that they are often helpless and even useless in turning a screw which has been fastened excessively tight. It is therefore, a common practice that a hammer is used to strike the head tip of the screw at work. Such a maneuver works at times in view of the fact that the combined effects of the striking force of the hammer and the torsional force of the screwdriver work to cause the screw to turn. However, if an excessive force is used in an attempt to turn such a tightly fastened screw as described above, the slotted head of the screw is bound to be damaged severely. In addition, it often requires an utmost skill to loosen a tightly fastened screw with one hand holding the hammer used to strike the head tip of the screwdriver and with another hand holding the screwdriver in action.